The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.
Not applicable.
The present invention relates to ink jet printing and in particular discloses a conductive PTFE bend activator vented ink jet printer.
The present invention further relates to the field of drop on demand ink jet printing.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
It is an object of the present invention to provide an alternative form of inkjet printer having an energy efficient nozzle actuator design which also can be simply constructed.
In accordance with a first aspect of the present invention, there is provided an ink jet nozzle comprising a nozzle chamber having an ink ejection port in one wall of the chamber, an ink supply source interconnected to the nozzle chamber and a thermal actuator activated to eject ink from the nozzle chamber via the ink ejection port, the thermal actuator comprising two layers of actuator material having a high coefficient of thermal expansion, a top layer being substantially non conductive and a bottom layer being conductive, the thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top layer, which is cooled by the chamber ink. Further, the bottom layer comprises portions being conductive and portions being non-conductive such that a circuit is formed for the heating of the bottom layer through the interaction of the conductive and non-conductive portions. Preferably, the resistive circuit is created having predetermined area of low circuit cross-sectional area so as to produce high levels of heating of the actuators in those areas. Advantageously, the non-conductive portions are formed from the same material as the top layer.
In accordance with a second aspect of the present invention, there is provided an ink jet nozzle comprising a nozzle chamber having an ink ejection port in one wall of the chamber, an ink supply source interconnected to the nozzle chamber and a thermal actuator activated to eject ink from the nozzle chamber via the ink ejection port, the thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top layer. Further, the bottom of the actuator can have a hydrophobic surface and during operation the hydrophobic surface causes an air bubble to form under the thermal actuator. The bottom surface of the actuator can be air vented so as to reduce the actuation energy required to eject ink from the nozzle chamber. Advantageously, the air venting comprises a series of small holes underneath the actuator, the holes being interconnected to an air supply channel for the supply of air to the back of the actuator. Further, the area around the bottom surface of the actuator can be constructed from hydrophobic material. The holes are of a size such that, during operation, any fluid is retained within the nozzle chamber. Preferably, the actuator is attached at one end to the nozzle chamber and the holes are located near the attached end and the actuator is constructed from polytetrafluoroethylene. Further, the actuator can have a bottom layer treated in portions so as to form a conductive material.